1. Field of the Invention
This invention relates to a microprocessor.
2. Description of the Prior Art
The use of a relatively small computer called "minicomputer" has been extended widely in recent years, mainly because of the advantage of incorporating the minicomputer into a system or device as one of its elements. The extension of the use of the minicomputer has been accelarated by its low cost. Another reason for this rapid spread of the minicomputer use is its applicability to general purposes which permit its utilization as a control element of a wide variety of relatively complicated systems each produced only in a small quantity. In other words, the minicomputer can be used more effectively, the more complicated the functions of the control element with which it is used. The present trend toward further extension of this type of computer demands a lower cost thereof, which in turn is leading to the advent of a microprocessor lower in grade than the minicomputer.
The microprocessor is intended to be incorporated in a device and it is not practical to be employed independently. It is necessary that the microprocessor, when incorporated in a device, provides a sufficiently superior matching with the other components of the device so that it competes well with a conventional control element. Therefore, the requirements of the microprocessor are the low cost and high flexibility or adaptability to other various component elements, which are contradictory to each other.
In an ordinary microprocessor, one word processesd therein consists of 8 to 12 bits and has a core memory of only 8K (8000) words or less. Such a microprocessor is used mainly as a programmable sequence control circuit for terminal equipment, automatic testing apparatus and sequence control device. The conventional microprocessors have no significant characteristics but have been constructed with the art similar to the one used for the minicomputers.